So the heat shield that I won on eBay for $50 looks really nice on the outside (except for a few tiny chrome blisters?) but the inside was really rusty so I soaked it in vinegar for almost a week and then scrubbed with low grit steel wool and what a difference! The tank came out looking really nice after the vinegar treatment but I left it alone overnight and now the surface rust on the inside is back. Same thing with the heat shield. the clean side was shiny just shortly before taking this pic. What can I do about the reoccurring surface rust?

The heat shields can do with a touch of VHT paint, after being washed in soap and water and wiped down with alcohol. I'm about 99% sure VHT makes a clear coat, but color might not matter too much since it's on the inside.

POR 15 works great but if there aren't any pinholes it's not really worth the fuss. When it's fully de-rusted, I always swish about 12 oz of premix around to coat the inside. Always keep the tank topped off with fuel while storing it to prevent further rust

Been a few years since I was working on my 360, but if I'm remembering things correctly, I think I ended up cutting mine off. The bearing race that's holding the rubber in place is pressed. In theory, you can just pull it off the stem, but I never had the correct tools to make it all happen.